Fix a simple typo (#1705)

Author: Delphn

src/v2/guide/syntax.md

@@ -102,7 +102,7 @@ These expressions will be evaluated as JavaScript in the data scope of the owner
 
 ## Directives
 
-Directives are special attributes with the `v-` prefix. Directive attribute values are expected to be **a single JavaScript expression** (with the exception for `v-for`, which will be discussed later). A directive's job is to reactively apply side effects to the DOM when the value of its expression changes. Let's review the example we saw in the introduction:
+Directives are special attributes with the `v-` prefix. Directive attribute values are expected to be **a single JavaScript expression** (with the exception of `v-for`, which will be discussed later). A directive's job is to reactively apply side effects to the DOM when the value of its expression changes. Let's review the example we saw in the introduction:
 
 ``` html
 <p v-if="seen">Now you see me</p>